The present invention relates to a tape cassette and, more particularly, to a lid for opening and closing a mouth portion of a tape cassette.
A tape cassette includes a lid to open and close a mouth portion of a front wall of a cassette housing. The lid of the tape cassette is composed of a front lid provided so as to open and close a front wall of a mouth portion, a top lid provided so as to open and close the upper portion of the front lid and a back lid provided at the rear portion of the front lid so as to become openable and closable.
An arrangement of a tape cassette having a lid composed of three lids will be described with reference to FIGS. 1 to 4. FIG. 1 of the accompanying drawings is a perspective view showing a tape cassette with a lid being closed. FIG. 2 is a perspective view showing the tape cassette with the lid being opened. FIG. 3 is a cross-sectional view showing a lid portion provided under the condition that the lid is closed. FIG. 4 is a cross-sectional view showing the lid portion provided under the condition that the lid is opened.
As illustrated, a cassette housing 1 is composed of an upper half 2 and a lower half 3. The cassette housing 1 accommodates a tape supply reel 4 and a tape take-up reel 5 so that the tape supply reel 4 and the tape take-up reel 5 can be rotated freely. A tape T supplied from the tape supply reel 4 is guided by a tape guide 7a supported to one opening portion 6a and transported along a mouth portion 8 of a front surface of the cassette housing 1. Then, the tape T is guided by a tape guide 7b supported to the other opening portion 6b and wound around the tape take-up reel 5.
A lid 9 is supported to the opening portions 6a, 6b and the mouth portion 8 of the cassette housing 1 so as to become freely rotatable. When the lid 9 is closed, the tape T transported along the front surface of the cassette housing 1 can be protected from being damaged.
The lid 9 will be described below in detail. The lid 9 is composed of three lids, i.e., a front lid 10 disposed so as to close the opening portions 6a, 6b and the front surface of the mouth portion 8, a top lid 11 disposed so as to cover the opening portions 6a, 6b and the upper portion of the mouth portion 8 and a back lid 12 disposed at the rear side of the front lid 10 and the top lid 11 within the mouth portion 8.
An arrangement of the lid 9 will be described. The front lid 10 can be opened and closed when rotary shafts 14, 14 provided on side surface plates 13, 13 are rotatably supported to the outer side surfaces of the lower half 3.
The top lid 11 includes a bearings 11a, 11a disposed at both front end side portions thereof and the bearings 11a, 11a are supported by upper respective side portions and support point shafts 15, 15. The top lid 11 includes first cam bosses 17, 17 disposed on the rear end portions of side surface plates 16, 16. The first cam bosses 17, 17 are movably engaged with first cam grooves 18, 18.
The back lid 12 includes shaft pins 12a provided on the upper end portions thereof. The shaft pins 12a are supported to bearings 11b, 11b formed on the rear surface of the top lid 11. Second cam bosses 20, 20 provided on side surface plates 19, 19 of the lower end of the back lid 12 are movably engaged with second cam grooves 21, 21 formed on the inner side surfaces of the mouth portion 8 which is composed of the lower half 3. The upper end portions of the second cam grooves 21, 21 are elongated up to the upper end portion of the mouth portion 8.
In the tape cassette thus arranged, under the condition that the lid 9 is closed, as shown in FIG. 3, the tape T transported along the mouth portion 8 is sandwiched between the rear surface of the front lid 11 and the lower end portion of the back lid 12.
Opening operation of the lid 9 will be described. When the tape cassette is accommodated to the loading position within a cassette compartment, if the front lid 10 is elevated by a member (not shown), the front lid 10 is upwardly rotated about the rotary shafts 14, 14 so as to be opened. Also, the top lid 11 that is supported by the support point shafts 15, 15 of the front lid 10 is rearwardly moved from the front ends to the rear ends of the cam grooves 18, 18 when the first cam bosses 17, 17 are guided by the first cam grooves 18, 18 on the upper half 2. Further, concurrently with the rearward movement of the top lid 11, the back lid 12 that is supported by the top lid 11 and the shaft pins 12a, 12a is elevated from the lower ends to the upper ends of the second cam grooves 21, 21 when the cam bosses 20, 20 are guided by the second cam grooves 21, 21. Thus, the lid 9 is opened as shown in FIG. 4.
The same assignee of the present application has already filed Japanese patent applications Nos. 57-277302 and 06-027561 (corresponding U.S. patent applications also were filed) and Japanese patent application No. 05-280704 (corresponding U.S. patent application and European patent application also were filed).
The shape of the second cam groove 21 along which the cam boss 20 of the back lid 12 is moved is limited by a pressure angle presented when the cam boss 20 is moved and a clearance provided between the tape T and the back lid 12. In particular, in the tape cassette in which the cassette housing is reduced in thickness, if the pressure angle is inhibited from being increased, then under the condition that the lid 9 is opened as shown in FIG. 4, the lid 9 is stopped at the position in which a part of the cam boss 20 of the back lid 12 is projected from the upper end portion of the second cam groove 21.
With the above-mentioned arrangement of the tape cassette, if the lid 9 that is in the opened state is applied with too large force of external force, then it is frequently observed that the cam boss 20 of the back lid 12 is disengaged from the upper end portion of the cam groove 21 as shown by phantom lines in FIG. 4. There is then the problem that the lid 9 cannot be closed in the closing operation of the lid 9.
To solve this problem, as shown in FIGS. 5 and 6, it is proposed that a retaining rib 22 is provided on the upper portion of the cam groove 21 in order to prevent the cam boss 20 from being disengaged from the upper end portion of the cam groove 21 when the back lid 12 is opened. When such retaining rib 22 is provided, an escape groove 23 has to be formed on the rear surface of the top lid 11 in order to prevent the rear surface of the top lid 11 from interfering with the retaining rib 22 under the condition that the lid 9 is closed.
However, the thickness of the retaining rib 22 should deliberately be set in order to avoid the occurrence of a problem that an escape portion becomes so-called short mold (flow of resin becomes insufficient) when the top lid 11 is formed by molding because the thickness of the top lid 11 at its escape portion is reduced by the escape groove 23 of the top lid 11. However, when a tape cassette is small in size, the thickness of the lid itself is comparatively thin and it is difficult to set the thickness of the retaining rib 22 to a proper thickness conforming to the preferable conditions.